It is conventional to use PLCs as controllers for industrial machines and the like. PLCs are configured by combining various units, for example, a power unit, which is a power source; a CPU unit, which centrally controls an overall PLC system; a motion CPU unit, which controls a servomotor via a servo amplifier attached to a drive unit of a production device or a facility device; an input unit, which receives signals of a switch or a sensor attached to an appropriate point on the production device or the facility device; an output unit, which transmits control signals to an actuator or the like; and a communication unit for connection to a communication network.
Before actually constructing a system, users need to carefully consider which units should be selected from the various units that are available, what layout is rational for the selected units, what setting is rational for relay relationships, etc. This is when users can use a system construction assistance apparatus.
System construction assistance apparatuses are capable of displaying a display object that corresponds to each unit at a designated position on a screen. Such a system construction assistance apparatus generates a system configuration diagram on the basis of the units represented by the display objects and the positions where they are placed. This allows the user to select units and consider the entire configuration of a system while referring to the generated system configuration diagram.
Here, the user needs to select units to be placed on the screen from many units when generating a system configuration diagram by using a system construction assistance apparatus. With regard to this point, when one unit is selected, a system construction assistance apparatus according to a technique described in Patent Literature 1, for example, predicts a unit that is likely to be selected following the selected unit on the basis of history and presents it to the user. This reduces the time taken by the user to search for a unit.